build: Don't complain about OpenJDK.

If we're supporting Java 7 (1.7??), we support OpenJDK. OpenJDK for Java 7 is ridiculously close to the Oracle JDK now, and I've been building with OpenJDK 7 for months anyway.

By the way, AOSP won't be supporting Java 6 (1.6???) anymore with the next release anyway, probably due to Java 6 being EOL'd.